Claims
- 1. A method of forming prefoamed beads with a crosslinking degree of 10 to 45% gel content, comprising the steps of:
- chemically crosslinking a starting bead-like polyethylene-base resin having a density greater than 0.940 g/cm.sup.3 to a crosslinking degree of 10 to 45% gel content;
- charging the crosslinked bead-like polyethylene-base resin, a foaming agent and a dispersion medium into a closed vessel;
- agitating and heating the resulting admixture at a temperature of from (the melting point of the resin -2.degree. C.) to (the melting point of the resin +30.degree. C.); and
- releasing the crosslinked bead-like polyethylene-base resin and dispersion medium into an atmosphere of a pressure lower than the internal pressure of the closed vessel thereby causing the crosslinked bead-like polyethylene-base resin to expand by an apparent expansion ratio in the range of from at least 15 to about 45.
- 2. A method as defined in claim 1 wherein said crosslinking step and said foaming step are performed in the same vessel.
- 3. A method as defined in claim 1 wherein said crosslinking step and said foaming step are performed in different vessels.
- 4. A method as defined in claim 1 wherein said crosslinking step includes adding a crosslinking agent to the starting polyethylene-base resin; dispersing the polyethylene-base resin and the crosslinking agent in a dispersing medium; and heating while simultaneously agitating the dispersion to a temperature sufficient to provide crosslinking.
- 5. A method as defined in claim 4 wherein said dispersing step includes adding a dispersing agent selected from the group consisting of particulate aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, and calcium carbonate.
- 6. A method as defined in claim 1 wherein said crosslinking step includes exposing the starting polyethylene-base resin to electron beams.
- 7. A method as defined in claim 1 wherein the polyethylene-base resin is selected from the group consisting of ethylene homopolymer, ethylene-propylene copolymer, ethylene-butene copolymer and ethylene-pentene copolymer.
- 8. A method as defined in claim 7 wherein said polyethylene-base resin contains ethylene in an amount of at least 95 weight-%.
- 9. A method as defined in claim 1 wherein the density .rho. of the starting polyethylene-base resin is in accordance with the following relation:
- 0.940 g/cm.sup.3 <.rho..ltoreq.0.970 g/cm.sup.3
- 10. A method as defined in claim 4 wherein said crosslinking agent is selected from the group consisting of dicumylperoxide, di-t-butylperoxide, t-butylcumylperoxide, .alpha.,.alpha.-bis(t-butylperoxy)-p-diiospropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane.
- 11. A method as defined in claim 4 wherein said crosslinking agent is added in an amount of 0.1-2.0 parts by weight per 100 parts of the polyethylene-base resin.
- 12. A method as defined in claim 4 wherein said heating step is performed at a temperature range of 130.degree.-180.degree. C. over a period of about 0.5 to 5 hours.
- 13. A method as defined in claim 4 wherein said dispersing medium is selected from the group consisting of water, ethylene glycol, glycerin, methanol, and ethanol.
- 14. A method as defined in claim 1 wherein the pre-foamed beads have an internal pressure decreasing velocity coefficient k of at most 0.35 at 25.degree. C. and 1 atm.
- 15. A method as defined in claim 1 wherein the foaming agent is carbon dioxide.
- 16. A method as defined in claim 1 wherein the foaming agent is selected from the group consisting of propane, butane, pentene, hexane, dichlorodifluoromethane, and dichlorotetrafluoroethane.
- 17. A method as defined in claim 1 wherein said foaming step includes adding the charging agent in an amount of 0.15-0.40 mole per 100 g of the bead-like resin.
- 18. A method as defined in claim 1 wherein said dispersing medium is selected from the group consisting of water, ethylene glycol, glycerin, methanol, and ethanol.
Priority Claims (1)
Number |
Date |
Country |
Kind |
58-198709 |
Oct 1983 |
JPX |
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Parent Case Info
This application is a continuation, of U.S. application Ser. No. 166,818 filed Mar. 1, 1988 which is a continuation of 842,121, filed Mar. 20, 1986 which is a continuation of 662,172, filed Oct. 18, 1984.
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Continuations (3)
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Number |
Date |
Country |
Parent |
166818 |
Mar 1988 |
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Parent |
842121 |
Mar 1986 |
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Parent |
662172 |
Oct 1984 |
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